In paper manufacture, an uneven strip, the so-called trim, is cut off from both edges of the paper before the latter is wound into rolls.
As the ever increasing slitter speeds have reached such levels as 2200 m/min and, even 2500 m/min, the removal of this trim from the locality where the slitting operation takes place has become a problem. Presently the trim removal from the slitter is effected either by means of an injector system or with a so-called chopper fan. Both of these work on the principle that the trim or its fragments are transported through a duct system under superatmospheric pressure.
In a system employing an injector, the trim strips are drawn from the slitter by means of an injector which cannot be spaced by more than a few meters from the slitter.
Disadvantages of this system are a high power consumption, a high noise level in the working area, and frequent malfunctioning caused by clogging of the duct. Moreover separate sets of equipment are usually required for the two ends of the paper roll.
In a chopper-fan arrangement the fan is located right beside the slitting station. The trim is drawn by the fan suction into the fan impeller and, being cut to pieces between cutting blades, travels in pieces along with an air stream through a duct system under superatmospheric pressure.
The disadvantages are the same as those of the injector system. Furthermore, when the cutting blades wear out and become blunt, the trim wraps around the impeller fouling the fan.